Recreational Clams in the Coos Estuary Summary: „„ Butter and Gaper Clam Populations in Some Areas of Lower Coos Estuary

Recreational Clams in the Coos Estuary Summary: Butter and gaper clam populations in some areas of lower Coos estuary

and South Slough have increased Butter clam Gaper since a similar assessment in the clam 1970s.

Native littleneck clams and cockle populations have generally fallen

since the 1970s in the areas sampled. Cockle Littleneck clam Population shifts of any estuarine-dependant animals should be cause for further investigation to understand potential causes of change. Source: ODFW 2014

Figure 1. 2009 ODFW SEACOR study areas located in the South Slough (SS) and Lower Bay (LB) subsystems.

What’s happening? Recreational clamming is an important part of our area’s quality of life. To improve understanding of clam population size and distribution in the Coos estuary, Oregon Department of Fish and Wildlife’s (ODFW) Shellfish and Estuarine Assessment of Coastal method (DAM) at three study sites: South Oregon (SEACOR) project documented in Slough, Clam Island and Pigeon Point. 2008-09 the status of four recreationally Rapid assessment method (RAM) data from important bay clam species in the lower Coos other sites (Empire, Airport and North Spit) estuary- South Slough (SS) and Lower Bay were deemed preliminary data only (see (LB) subsystems (see Figure 1): gaper clams Background). Italicized text below indicates (Tresus capax); butter clams (Saxidomus sections quoted directly from the ODFW gigantea); native littleneck clams (Leukoma (2014) report unless otherwise noted. staminea); and cockles (Clinocardium nuttallii). SEACOR Study Results Project scientists estimated the distribution Clam beds were found in all areas studied by and abundance of each species within the SEACOR team. The greatest numbers of the SEACOR study sites and described the clam beds were found at the Clam Island and habitat requirements for each. The results Pigeon Point study sites (both in the Lower of this work are summarized in Table 1 Bay subsystem)(Figure 1). Overall, both gaper (ODFW 2014). The ODFW report summarizes clams and butter clams were found in much results from their detailed assessment greater densities than cockles and littleneck clams at all study sites (Table 1). Gaper clam Table 1. Mean clam density data per meter squared densities were the highest at the Clam Island for three SEACOR study areas in the lower Coos estuary. ODFW 2014. study site (Figure 2, Table 1) and butter clam densities were high at both Clam Island and Pigeon Point (Figure 3, Table 1), which are both located in the lower Coos estuary subsystem. Cockles were found in relatively high densities only in the South Slough study area (Figure 4, Table 1), while native littleneck clams were found only in low densities at all three sites, the most dense being Pigeon Point (Figure 5, Table 1).

The low densities of littleneck clams in the 2009 SEACOR study contrasts with earlier surveys conducted in the 1970s when native littleneck clams were found to be reasonably abundant in the Coos estuary. Figure 2. Gaper clam abundance and distribution in SEACOR Figure 3. Butter clam abundance and distribution in SEACOR study areas Data from Empire, Airport and North Spit sites are study areas. Data from Empire, Airport and North Spit sites are considered preliminary only. Data: ODFW 2014. considered preliminary only. Data: ODFW 2014.

Figure 4. Cockle abundance and distribution in the SEACOR Figure 5. Littleneck clam abundance and distribution in the study areas. Data from Empire, Airport and North Spit sites are SEACOR study areas. Data from Empire, Airport and North Spit considered preliminary only. Data: ODFW 2014. sites are considered preliminary only. Data: ODFW 2014. Additional detail, organized by study sites, is found in ODFW’s SEACOR final report (2014):

Clam Island supported high densities and diverse assemblages of bay clams (Figure 6). Butter clams were abundant across all tidal strata at Clam Island (site mean=4.6 clams/m2). Cockles were least abundant at Clam Island, compared to the other tide flats surveyed by DAM, and were most abundant in the mid-intertidal (mean = 0.6 clams/m2). Gaper clams exhibited the greatest densities at Clam Island (mean=19.9 clams/m2) and were most dense in the low intertidal (mean=45.6 clams/m2). Native littleneck clams exhibited low densities at all three sites 2 2 Figure 6. Clam distribution and abundance (clams/m ) at the (mean=0.7 clams/m ), including Clam Island SEACOR Clam Island study site. Note the difference in scale for (mean=0.4 clams/m2). each clam species. Data are from DAM surveys only. Data and figure: ODFW 2014.

Pigeon Point exhibited the highest densities of butter clams (Figure 7), particularly at high tidal elevations (H, mean=15.0 clams/m2) in sandy areas commonly referred to as “butter bars.” Cockles were not very abundant at Pigeon Point (mean=1.0 clams/m2), and were most prevalent in the mid tidal stratum at Pigeon Point (mean=2.2 clams/m2). Gapers were less abundant at Pigeon Point compared to Clam Island (mean=3.1 clams/m2). Low tidal elevations harbored the greatest densities of gapers across all sites (mean=19.3 clams/ m2) including Pigeon Point (mean 8.2 clams/ m2). Littleneck clams exhibited the highest densities at Pigeon Point (mean=1.4 clams/ m2), where they showed little difference in density among tidal strata. Figure 7. Clam distribution and abundance (clams/m2) at the SEACOR Pigeon Point study site. Note the difference in scale for each clam species. Data are from DAM surveys only. Data and figure: ODFW 2014. South Slough exhibited the lowest density of butter clams (mean=2.1 clams/m2), but they were still abundant compared to other clams such as cockles and littlenecks (Figure 8). The highest densities of cockles occurred at South Slough (mean=1.5 clams/m2), particularly in high and low tidal elevations (mean=2.0 clams/m2 and 1.6 clams/m2, respectively). The largest cockles were also collected at South Slough (mean shell length=70.2 mm). Gapers were least abundant at South Slough (mean=1.8 clams/m2) among the three sites sampled by DAM. Generally, gaper clam length increased with decreasing tidal stratum except at South Slough, which lacked smaller gaper clams. Littleneck clams were least abundant at South Slough (mean=0.3 clams/m2)(Figure 8) and were entirely absent at many waypoints surveyed by DAM. Figure 8. Clam distribution and abundance (clams/m2) at the SEACOR South Slough study site. The scale for each clam species is the same. Data are from DAM surveys only. Data and figure: ODFW 2014. Clam Bed Attributes Clam bed attributes including bed type, eelgrass cover, sediment type and intertidal • Cockles and littleneck clams were most elevation were measured by ODFW scientists frequently found in oxygenated clam bed and summarized for the Coos estuary in Fig- sediments. ures 9-12. They determined through a series • The presence of gaper clams was neg- of regression analyses the following: atively correlated with sediment tem- • The presensence of algae on clam beds perature “at depth” (the depth in the was negatively correlated with the pres- sediment where those clams are normally nce of butter clams- these clams were found). So, the higher the sediment tem- almost always found in non-vegetated peratures were, the fewer gaper clams sand flats. were found. Gapers were found in greatest abundances in low intertidal flats. • The presensence of algae in clam beds was positively correlated with the pres- • The presence of native eelgrass beds nce of cockles and with the presence of (Zostera marina) was positively correlated gaper clams. with the presence of littleneck clams (in the few areas they were found). Figure 10. Major sediment type in the SEACOR study areas. Data: ODFW 2014. Figure 9. Intertidal bed type in the SEACOR study areas. Data: ODFW 2014.

Figure 11. Eelgrass cover in the SEACOR study areas. Data: Figure 12. Tideal height range in the SEACOR study areas. Data: ODFW 2014. ODFW 2014. Why is it happening?

The status of clam populations is a function of a variety of environmental conditions including but not limited to bathymetry (shape of the estuary bottom), human activities (e.g., commercial oyster culture, dredging of the commercial shipping channel), and the health of other key benthic and pelagic communities such as eel grass beds and crustaceans (Carl- ton et al. 1991; Yocom and Edge 1929).

Furthermore, the status of local environmental conditions is determined by many chang- ing elements associated with both natural and human-induced changes. For example, the effects of major storms or the establish- ment of an oyster culture system have the po- Figure 13. Locations of all previously conducted clam surveys tential to change the bathymetry of an area in Coos Bay via sedimentation or scouring of the estuary bottom. These same actions may also affect the health of nearby eelgrass communities Detailed comparisons between studies (Carlton et al. 1991). Determining the effects conducted during different time periods are of these activities is a complicated process made difficult by gaps in the data. For exam- requiring collection of quanitative data over ple, only two published clam surveys of Pony multiple time periods. Slough have been completed, with the most recent data coming from the 1970s (Macdon- Past Studies ald 1967; Bottom et al. 1979). Additionally, Previously conducted clam research in the some areas such as the Upper Bay subsystem, Coos estuary provides information that can for which the Marriage study (1958) rep- be used to characterize trends in local clam resents the most current data, have not been populations. The research presented here surveyed for many years. Methodological represents 80 years of published clam survey differences between studies further compli- data. The oldest study dates back to 1929 cate comparisons between data sets from and the most recent study was completed different studies. in 2009. Figure 13 provides a geographic summary of the study areas for all previously These difficulties notwithstanding, the published clam surveys in the Coos estuary. available historic data are useful in that they provide a snapshot of the status of clams over (e.g., exposure to ocean waves, varying levels time. Comparisons of historic data may be of tidal current and sedimentation, etc.) each valuable in instances where methodological area studied exhibited high biodiversity, with differences in and of themselves are unlikely twenty-seven different species of bivalves oc- to account for overwhelmingly clear trends curring between Coos Head and Fossil Point over time. alone (Figure 15).

Historically, clams have demonstrated a wide Some historic trends in local clam populations range of adaptations to the environmental are apparent. The decline of soft shell clams conditions of the study area. In 1929, Yo- (Mya arenaria) between the 1920s and the com and Edge observed a total of forty-one 1950s is apparent when comparing the find- bivalve species in the area between Sunset ings of Yocom and Edge (1929) with those of Bay and Fossil Point (Figure 14). Despite Marriage (1958). having surveyed a variety of substrata (e.g., rocks, sand, mud, mixed sand and mud, and Yocam and Edge noted an abundance of soft driftwood) with diverse habitat characteristics shell clams in South Slough in 1929 while Marriage found no soft shelled clams in the same area nearly thirty years later.

Marriage also surveyed North Slough and Haynes Inlet, where soft shell clams were found in scattered beds. It should be noted that the North Slough and Haynes Inlet soft shell clam populations were much smaller than those of earlier years in the same areas, Figure 14. Survey area for Yocom and Edge (1929) is highlight- suggesting that the pattern of population ed above in green. decline may well have been characteristic of the greater Coos estuary during these years (Marriage 1958).

In the case of butter and gaper clams at Pi- geon Point and Clam Island, the data suggest that the populations of these species may have decreased since the 1970s (Figures 16 and 17). This decline is due to a decrease in clam abundance on Clam Island; although Figure 15. Relative diversity of clams in three inventory subre- the decline is partially offset by increases at gions. CH = Coos Head SS = South Slough FP = Fossil Point Data: Yocom and Edge 1929. Pigeon Point and may be subject to some variation in magnitude due to methodological Background differences across studies, it seems likely that SEACOR Study the net effect is negative (ODFW Shellfish From the SEACOR report summary (ODFW Program 2009). 2014, unless otherwise noted):

SEACOR is funded by Oregon Department of Fish and Wildlife recreational shellfish license fees and captures a snapshot of the status of Oregon’s estuarine resources for baseline data and for comparison to past (ODFW 1970’s “raccoon” report: Bottom et al. 1979) and future studies. The SEACOR project initially targeted intertidal flats of the lower Coos Bay Estuary during 2008-2009. Howev- er, the state legislature has made the project permanent to allow future assessment of all of Oregon’s estuaries following this general Figure 16. Gaper clam abundance data from a 1979 report sampling strategy (ODFW Shellfish Program (A) are compared to the same data from a study conducted in 2009 (B). Data: ODFW 2014. 2009).

Coos Bay was selected as SEACOR’s pilot site because it is Oregon’s largest outer coast estuary, has a long history of supporting recreational and commercial clam harvest, and has experienced increasing urbanization and industrialization since the late 1800s. Coos Bay is a proposed site for a large liquid natural gas facility which would require additional dredging of the channel, an activity that first occurred in 1927. The increasing importance

Figure 17. Butter clam abundance data from a 1979 report of Coos Bay as a shipping port since its early (C) are compared to the same data from a study conducted in colonization resulted in physiographic chang- 2009 (D). Data: ODFW 2014. es primarily from dredging and filling as well as community compositional changes from introductions and extractions. Updating our understanding of estuarine habitats and the distribution and size of Coos Bay bay clam populations was valuable and necessary in the face of these changes in habitat and com- on three sides and a section of the shoreline munity structure. that extends south. On the northern border of the Airport runway, there is an extensive, san- This 18-month study focused on six study sites dy, shrimp-dominated tide flat. To the west which encompassed three tidal strata (low, of the Airport, there is a heterogeneous and mid, high)(Figure 1). These sites were iden- broad tide flat that forms a small peninsula. tified by a “scouting” method not employed The peninsula is composed of soft mud close with the subsequent estuary studies. Scouting to the runway and to the east, sand at the was accomplished using a team transect ap- western edge, a small terrestrial island in the proach. Team members spaced 10 m apart re- center, and a mixed sediment eelgrass habitat corded habitat information every 10 m along to the far south. transects from shore to channel. The team was repositioned every 100-300 m along the The Clam Island study site is emergent only at shore of lower Coos Bay. Based on scouting, lower tides and is entirely isolated from land study sites were selected for sampling when by water during all tides. It is bordered by an the following criteria met: (1) the area was unmaintained channel to the west (demarcat- composed of unconsolidated sediment suit- ed by pole markers at the north and south end able for burrowing organisms, (2) the area of the island) and by the federally-maintained was located in the marine-dominated region navigational channel to the east. The south- of the estuary (Davidson 2006), (3) the area ern end is lower in tidal elevation than the was large enough to support a statistically northern end, and there is a depression at the viable number of samples, (4) the area was southern end with abundant eelgrass. This known to be or likely to be used by recreation- study site is a popular target of recreational al shellfish harvesters, and (5) the area was clammers, and the adjacent channels are pop- likely to support clam species at some popu- ular for recreational crabbers, as well. lation level, based on previous studies. This last criterion highlights a key change made for The Empire study site is a relatively narrow future estuarine studies. Entire tidal flats were strip of two distinct tide flats partially sepa- surveyed in Tillamook Bay instead of target- rated by a small dune headland. The larger ing clam bed areas as was done for the Coos portion of this site is to the south and the Bay pilot study. entire site is bordered to the east by low-lying dunes and densely-urbanized variable neigh- The six study sites are described by ODFW borhood. (2014) as follows: The North Spit study site is dominated by The Airport study site is composed of several four cobble-dominated terrestrial islands, contiguous extensive tide flats that border the surrounded by areas of soft mud and other Southwest Oregon Regional Airport runway areas of sand. The western border is the sand peninsula that encloses Coos Bay. The dune and by the lightly-developed forested bluff area to the north of the study site was light- known as Collver Point, to the south. There ly-developed with industrial buildings, and is a large cluster of hummocks (raised ar- is a natural area with limited public access eas), vegetated with salt marsh plants that (i.e. four-wheel drive on sand or boat access are entirely submerged only at extreme high only). This lightly-developed industrial area tides. There are also two major drainage to the north (Jordan Cove, specifically) is the channels from the Metcalf Marsh, one to the proposed location of a new liquid natural gas south and one to the north of the hummock facility. cluster. There is abundant eelgrass (Zostera marina) in the lower intertidal areas. This site The Pigeon Point study site is the most het- is a very popular area for clammers. It is also erogeneous, with separate areas dominated subject to harvest by small-scale commercial by cobble, nearly pure sand, and nearly pure clammers harvesting cockle clams, and other mud. There are several dredge spoil piles that fishermen harvesting burrowing shrimp for are not emergent at standard high tides com- bait. The South Slough study site also includes posed largely of cobble that form a barrier the smaller “Charleston Triangle” and “Fish- across the edge of the site; this separates the erman’s Grotto” (a restaurant at the access bulk of the exposed tide flat from the shipping point) tide flats, which were only sampled channel. There are two permanent pools, one during RAM surveys. Both of these tide flats to the north that is shallow and is highly veg- are located just north of the Charleston etated with eelgrass and algae and a second Bridge, are heavily used by clammers, and are pool in the central area that is filled with soft adjacent to the marina and fish processing mud and light vegetation. This site is named plants. after “Pigeon Point,” a highly-developed residential neighborhood that borders the south This study assessed 450 ha of tide flats of edge. The eastern edge is also highly-devel- which 150 ha were surveyed by DAM. RAM oped with residential buildings. In contrast, surveys were conducted at all 6 study sites, the northern border is a low-lying dune hab- whereas DAM surveys (n=45 sites) were only itat situated on landfill. Access to this site is conducted in Clam Island, Pigeon Point, and fairly easy, with paths leading down the bluff South Slough. The SEACOR results focus on face at both the northern and southern ends. these three flats. All results are detailed in the SEACOR Coos Bay Final Report (in prep.). The South Slough study site refers to an area that contains three discrete tide flats with the largest of the three locally called the “South Slough Flat”. The “South Slough Flat” is bordered by the Charleston Bridge at its northern edge, the Metcalf Marsh at its western edge References Oregon Department of Fish and Wildlife (ODFW). 2014. Status of Oregon bay clam Bottom, D., B. Kreag, F. Ratti, C. Roye, and R. fisheries, stock assessment, and research. Starr. 1979. Habitat classification and inven- [Information Report Series draft June 2014]. tory methods for the management of Ore- Oregon Department of Fish and Wildlife Ma- gon estuaries. [Oregon Department of Fish rine Resources Program. 113 pp. and Wildlife final estuary inventory project report]. 84 pp. Yocom, H. B. and E. R. Edge. 1929. The ecolog- ical distribution of the Pelecypoda of the Coos Carlton, J. T., G. M. Ruiz, and R. A. Everett. Bay region of Oregon. Northwest Science: 1991. The structure of benthic estuarine 65-71. communities associated with dense suspend- ed populations of the introduced Japanese oyster Crassostrea gigas: years 1 and 2. [South Slough National Estuarine Research Reserve final report]. United States Depart- ment of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, Office of Ocean and Coastal Resource Management, National Estuarine Research Reserve System. Washington, DC.

Davidson, T. M. 2006. The invasion of the Australasian burrowing isopod (Sphaeroma quoianum) in Coos Bay, Oregon. University of Oregon.

Hancock, D. R. 1979. Subtidal clam populations: distribution, abundance, and ecology. Oregon State University, Sea Grant College Program. Corvallis, OR.

MacDonald, K. B. 1967. Quantitative studies of salt marsh mollusc faunas from the North American Pacific Coast. [PhD Thesis]. Univer- sity of California. San Diego, CA.

Marriage, L. D. 1958. The bay clams of Ore- gon; their identification, relative abundance, and general distribution. Fish Commission of Oregon. Portland, OR.

Oregon Department of Fish and Wildlife Shell- fish Program. 2009. SEACOR Results. Available online http://www.dfw.state.or.us/mrp/shellfish/Seacor/results.asp